[PATCH} mm: Merging memory blocks resets mempolicy

[Hampson, Steven T]

Using mbind to change the mempolicy to MPOL_BIND on several adjacent
mmapped blocks
may result in a reset of the mempolicy to MPOL_DEFAULT in vma_adjust.

Test code.  Correct result is three lines containing "OK".


#include <stdio.h>
#include <unistd.h>
#include <sys/mman.h>
#include <numaif.h>
#include <errno.h>

/* gcc mbind_test.c -lnuma -o mbind_test -Wall */
#define MAXNODE 4096

void allocate()
{
        int ret;
        int len;
        int policy = -1;
        unsigned char *p;
        unsigned long mask[MAXNODE] = { 0 };
        unsigned long retmask[MAXNODE] = { 0 };

        len = getpagesize() * 0x2fc00;
        p = mmap(NULL, len, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
                 -1, 0);
        if (p == MAP_FAILED)
                printf("mbind err: %d\n", errno);

        mask[0] = 1;
        ret = mbind(p, len, MPOL_BIND, mask, MAXNODE, 0);
        if (ret < 0)
                printf("mbind err: %d %d\n", ret, errno);
        ret = get_mempolicy(&policy, retmask, MAXNODE, p, MPOL_F_ADDR);
        if (ret < 0)
                printf("get_mempolicy err: %d %d\n", ret, errno);

        if (policy == MPOL_BIND)
                printf("OK\n");
        else
                printf("ERROR: policy is %d\n", policy);
}

int main()
{
        allocate();
        allocate();
        allocate();
        return 0;
}

Signed-off-by: Steven T Hampson <steven.t.hamp...@intel.com>


---

diff --git a/mm/mmap.c b/mm/mmap.c
index 8832b87..5ba8b92 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -820,7 +820,7 @@ again:                      remove_next = 1 + (end > 
next->vm_end);
                if (next->anon_vma)
                        anon_vma_merge(vma, next);
                mm->map_count--;
-               mpol_put(vma_policy(next));
+               vma_set_policy(vma, vma_policy(next));
                kmem_cache_free(vm_area_cachep, next);
                /*
                 * In mprotect's case 6 (see comments on vma_merge),

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